The present invention relates generally to methods and apparatus for increasing the ability of pilots of high performance aircraft to resist high G caused unconsciousness, and more specifically to a novel method for controlling the aircraft to prevent high G caused unconsciousness.
While flying simulated or actual combat maneuvers, a fighter pilot's body undergoes very high accelerations from the rapid changes in speed and direction. These accelerations are generally expressed in units of G, equal to the acceleration of a mass at the surface of the Earth due to gravity. The accelerations of greatest concern to a pilot are those that occur along the vertical z-axis of the cockpit when the pilot pulls back hard on the aircraft control stick to accomplish a rapid climb or a fast banked turn. The pilot's oxygen-carrying blood is forced away from its regular path between the heart-lungs and the brain, and pools toward the blood vessels of his lower extremities. At sufficiently high G's, the pilot's field of vision narrows as blood flow to the retinas is reduced, or grayout, followed by blackout, and finally followed by loss of consciousness from insufficient blood flow to the brain.
Pilots fight the effects of high G's by straining maneuvers, tensing the muscles of their torso and extremities to squeeze shut the blood vessels and force blood flow to continue in the upper parts of their body. An anti-G suit helps this process by covering the pilot's legs and torso with air bladders which are automatically inflated during high acceleration maneuvers to compress the blood vessels in those regions and force blood flow to continue to the brain. Because continuous compression of the blood vessels of the lower extremities is harmful, anti-G suits include an anti-G valve to restrict inflation only to periods of high acceleration.
Modern high performance jet fighters, such as an F-16, increasingly incorporate computer controlled intelligent flight control, or fly-by-wire, systems. In an F-16, the pilot indicates through control stick movement a request for a maximum rate maneuver and the flight control system computer determines and commands the appropriate response. The flight control computer limits the severity of its commands to restrict the maximum G loading on the aircraft. Generally, the maximum permitted G loading is well beneath the capabilities of the airframe and is intended to restrain the G loadings to levels that an experienced pilot can tolerate. This computer controlled limiting of maximum G loadings has not been completely successful in protecting pilots from blackouts. The nearly instantaneous response of a high performance aircraft causes acceleration onset rates((dG/dt or G') greater than the response time of typical anti-G suit valves, leaving the pilot both unprotected for periods of time sufficient to cause unconsciousness, and causing unconsciousness due to a high onset rate of acceleration at G levels lower than the pilot could otherwise tolerate.
The prior art has attempted to solve these problems primarily by improvements in anti-G valves to improve response times. See, for example, U.S. Pat. No. 3,780,723 to the present inventor, co-pending application No. 831,901 to the present inventor U.S. Pat. Nos. 4,243,024 to Crosbie et al, and 4,336,590 to Jacq et al.
The present emphasis on fast response anti-G valves, while valuable in solving the dangers of high onset rate acceleration, has largely ignored the ability of pilots to tolerate for short periods much higher G-levels than flight controls presently permit. Current high performance aircraft are capable of maneuvering at accelerations of 9 G. The perceived limits of maximum permissible acceleration on pilots using current anti-G equipment and seat configurations is approximately 7 G, which defines the outmost boundary of performance permitted by present fly-by-wire systems. Experiments show that pilots can tolerate accelerations over 8 G if limited in duration to less than 3 seconds. It is seen, therefore that the operational performance of these aircraft is capable of being enhanced by a ratio of 9:7, or almost 29%.
It is, therefore, a principal object of the present invention to provide a significant extension of the usable flight envelope of a fighter aircraft without danger of causing a sudden G-induced loss of pilot consciousness.